Mechanisms underlying the effects of ethanol on the synaptic activity are, in large part, believed to involve inhibition of NMDA receptors and potentiation of GABAA receptors. Adaptive change in response to depressed synaptic activity are believed to underlie the development of acute and chronic tolerance. The mechanisms by which this is accomplished have yet to be determined. The proposed studies herein are intended to evaluate ethanol's effects on synaptic plasticity by examination of NMDA, AMPA and GABAA receptor organization in the synapse, as well as changes in dendritic spine motility and number. This will be accomplished with the use of cultured hippocampal neurons after acute or chronic exposure to ethanol. These studies will involve the following specific aims: 1) Investigation into the effects of ethanol on the synaptic localization and membrane expression of AMPA and NMDA receptors; and 2) Examination of the membrane expression of GABAA receptors with ethanol. These experiments will include immunohistochernical measures for synaptic clustering and biotin labeling for assessment of membrane expression. Electrophysiological correlates for functional changes in AMPA and NMDA receptors will be measured as well. 3) Dynamic changes in dendritic spine shape and number in response to ethanol will be investigated as well. These studies will use the expression of an actin- GFP fusion protein for the visualization of individual dendritic spines. Elucidation of this functional process will greatly contribute to our understanding of how alcohol alters brain function.